An access protocol based on contention in 802.11 (being a wireless local area network standard initially formulated by IEEE) standard constitutes the basis of 802.11 media access control (referred to as MAC) protocol, and the standard specifies a distributed coordination function (referred to as DCF) for a contention phase for the media access control layer (MAC) of the WLAN. The DCF uses the technology of Carrier Sense Multiple Access with Collision Detection (referred to as CSMA/CA) to detect a media state by means of physical and virtual carrier sense functions, and each terminal may independently determine to access a channel and enter into a back-off process when the access is failed so as to reconnect the channel, thereby providing a more flexible wireless communication manner.
In the wireless communication field, each terminal may independently determine to enter into the channel and enter into the back-off process when the access is failed so as to reconnect the channel. However, only one shared channel exists in the wireless local network, and therefore, a station with services to be sent needs to perform channel contention; when stations participated in channel contention are sensed to be idle, duration of a distributed coordination inter frame space (DIFS) is delayed, and a random back-off duration is further waited, and if the channel is still idle at the moment, then the channel is accessed. The random back-off duration is also called a contention window (CW), and in order to reduce the collision probability; the size of an optimal contention window depends on the quantity of stations participating in channel contention in a channel at the same time slot. If the number of stations participated in the contention is less, then the collision probability is low, and now a smaller contention window may be used so as to reduce delay; and if the number of stations participated in the contention is much, then the collision probability is high, and now it is suitable to use a larger contention window so as to reduce collision and improve throughput of the whole network.
In a wireless local area network standard, a back-off method of binary index in a unit of time slot is usually used to acquire a contention window value, and CW is a random integer selected from equal distribution on the section [0, CW−1], and CW ε [CWmin, CWmax], and during retransmission for an ith time, CW(i)=min[2i·CWmin, CWmax], and min( ) represents taking a minimum value within brackets. The CW is reset to be CWmin after being sent successfully every time. However, in the case of network congestion, if the CW is reset to be CWmin after successful sending, it would easily cause collision and retransmission, and reduce network throughput; and in the case of network congestion being relieved, the transmission would be doubled and the number of network idle time slots would be increased, and unnecessary delay would be introduced and the network throughput would be reduced.